Controlling size of Items in Qml Styles

Hi all,
I'd like to create my own styled RadioButton, but I'm having difficulty controlling the size of the components used in the RadioButtonStyle that I am using. I want to put my RadioButton in a GridLayout and have the RadioButton take up all the available space (as if I were setting Layout.fillWidth and Layout.fillHeight to true)

To start off with, I am using the RadioButtonStyle code from the Qt docs inside a GridLayout: